Diffusion transfer process

ABSTRACT

IN A SILVER COMPLEX DIFFUSION TRANSFER PROCESS, AN IMPROVED PURE BLACK COLOR TONE AND RAPID TRANSFERABILITY ARE SIMULTANEOUSLY ATTAINED BY CARRYING OUT THE DEVELOPMENT IN THE PRESENCE OF TONERS, SELECTED FROM COMBINATIONS OF A LEAST ONE OF 3-ALKYLBENZOTHIAZOLINE-2-THIONE DERIVATIVES (A) AND AT LEAST ONE OF 2-MERCAPTO-1,3,4OXADIAZOLE DERIVATIVES (B).   2-(S=),3-R1,R2-2,3-DIHYDROBENZOTHIAZOLE (A)   2-(HS-),5-R3-1,3,4-OXADIAZOLE   WHEREIN R1 IS AN ALKYL GROUP HAVING NOT MORE THAN 5, R2 IS HYDROGEN, ALKYL GROUP HAVING NOT MORE THAN 3 CARBON ATOMS OR ALKOXY GROUP HAVING NOT MORE THAN 3 CARBON ATOMS, AND R3 IS AN ALKYL GROUP HAVING NOT MORE THAN 8 CARBON ATOMS, ARYL OR SUBSTITUTED ARYL GROUP.

United States Patent O 3,702,246 DIFFUSION TRANSFER PROCESS Yasushi Ohyama, Takatsuki, and Kiyoshi Futaki and Senji Tosa, Kyoto, Japan, assiguors to Mitsubishi Paper Mills, Ltd., Tokyo, Japan No Drawing. Filed Apr. 15, 1970, Ser. No. 28,989 Claims priority, application Japan, Apr. 16, 1969, 44/29,042 Int. Cl. G03c 5/52 US. CI. 96-29 R Claims ABSTRACT OF THE DISCLOSURE In a silver complex diffusion transfer process, an improved pure black color tone and rapid transferability are simultaneously attained by carrying out the development in the presence of toners, selected from combinations of at least one of 3alkylbenzothiazoline-Z-thione derivatives (A) and at least one of 2-mercapto-1,3,4- oxadiazole derivatives (B),

wherein R is an alkyl group having not more than 5,

R is hydrogen, alkyl group having not more than 3 carbon atoms or alkoxy group having not more than 3 carbon atotms, and R is an alkyl group having not more than 8 carbon atoms, aryl or substituted aryl group.

This invention relates to an improved silver complex diffusion transfer process using a photosensitive silver halide emulsion.

The so-called silver complex diffusion transfer process has been used not only for copying, but also for ordinary photography, by which positive prints are directly and rapidly obtained. Furthermore, recently it has been widely used as a business copying system, according to which publications are rapidly copied in a black-and-white positive form by one procedure. The blackness, color tone and black-and-white contrast of the obtained images are excellent and satisfactory copies can be rapidly obtained even from coarse originals. However, obtainment of silver images having a pure black tone and acceleration of development and transfer are not necessarily compatible and it has been difficult to improve further the rapidity of development.

In an initial stage in the investigation of the diffusion transfer process, the color of metallic silver which is separated by reduction of a silver complex in a receiving layer was found to be yellow or brown and the color tone had to be converted to a blackish tone by gold or selenium toning. Then, it was found that the color tone of reduced silver images can be improved by adding to a developer, photosensitive layer or receiving layer a small amount of organic additives such as mercapto benzothiazole, phenylmercapto tetrazole, etc. which are known as anti-foggants for ordinary silver halide-emulsions. However, generally such agents cause the reduction of solubility of silver complex and hence, both transfer speed and developing speed (for both negative and positive) of silver salt or silver complex are usually significantly decreased. Thus, not only transfer and development speeds are decreased, but also the density of the images is reduced. Therefore, even if black images can be obtained,

3,702,246 Patented Nov. 7, 1972 ICC only such images as having low density are formed due to a slight excess of the said agents.

Thereafter, various compounds such as benzylamine, fl-phenylethyl amine, N-dodecyl pyridium salts, similar picolinium salts, hydrazines, etc. have been proposed as materials to increase the developing speed. However, since these materials generally have an adverse effect on color tone, they have been used together with benzotriazole, 5-nitrobenzirnidazole or phenyl mercapto tetrazole which have been known as so-called blue black developers and which can improve color tone, but decrease developing speed.

Recently, those materials which accelerate development and simultaneously improve color tone have been found in ordinary photographic development. Illustrative thereof are 5,5 dimethyl 2 thiohydantoin, 5 benzylidene- 1,3 ozazolidin 4 one 2 thione or 5 methyl- 3 mercapto 1,2,4 triazole. However, although those which are called blue black toner materials can result in formation of blue black images in the case of chemical development of silver chloride emulsion, they do not have much effect with silver bromide emulsion. Furthermore, when a silver halide solvent such as sodium thiosulfate is present in a developer, the development accelerators show only a slight or no effect. In a silver complex diffusion transfer process, the developer contains a silver halide solvent such as sodium thiosulfate and moreover in a positive transfer layer there is operating, instead of chemical development, a kind of physical development in which a soluble silver complex is reduced at the surface of nuclei. Therefore, the above mentioned materials which are development accelerating toners in chemical development will not necessarily improve the color tone of images in a diffusion transfer process.

The basis of this invention concerns the use of additives capable of forming a definite image having pleasant pure black or blue black color tone and showing no metallic luster and furthermore capable of providing rapid transfer in a diffusion transfer process.

The compounds which have the following structural Formula I and which once proposed for use as a blue black developing additive by the inventors display an excellent color tone effect.

R and R are lower alkyl groups, and R" is hydrogen, lower alkyl, methoxy, ethoxy or halogen). However, many of the said compounds, when used in a diffusion transfer process, show poor color tone and do not accelerate transferability. As a result of various researchs, it has been found that those compounds having the following general structural formula (A), namely, 3-alkylbenzothiazoline-2- thione derivatives can provide relatively excellent color tone and furthermore can accelerate transfer among the compounds having the structural Formula I.

(wherein R is an alkyl group having not more than 5 carhon atoms and R is hydrogen or alkyl or alkoxy group having not more than 3 carbon atoms).

However, these compounds still have the defect that although rapid transfer may be attained, stain of the white ground tends to occur. The stain of the white ground may be prevented by using the well known Z-mercaptobenzothiazole, 1-p'henyl-5-mercapto-l,2,3,4-tetrazole, etc. together with said compounds (A) and increasing the degree of exposure. However, in general, these compounds restrain the transfer speed and hence, cause the loss of the excellent transferability which is attained by the said compounds (A). Furthermore, there is a limitation to the amount of the said mercapto compounds to be used together with the compounds (A).

As a result of intensive research, it has been found that 2-mercapto-l,3,4-oxadiazole derivatives having the following general structural Formula B are especially suitable for combined use with the compounds (A) to improve both color tone and transferability.

(wherein R is alkyl, aryl or substituted aryl group having not more than 8 carbon atoms).

Among the said derivatives (B), those in which R, is methyl, ethyl, propyl, amyl, phenyl or substituted phenyl such as Z-methylphenyl, 3-ethylphenyl, or 4-methoxyphenyl are easily synthesized and furthermore are especially effective. These compounds (B) show a somewhat restraining action on transferability, but have an effect of imparting pure black or blue black tone. Especially, no impairment of transferability is caused in spite of the fact that combined used of compounds (B) with compounds (A) results in an improvement of color tone and density and removal of stains in a white ground. When the number of carbon atoms exceeds the upper limit, water-solubility of the compounds (B) is decreased and the restraining action of transferability is more marked.

As explained above, by using a combination of compounds (A) and (B), this invention is able to attain balanced properties of excellent color tone, density, transfer speed and stainless white ground as well as a compensation of defects of the compounds (A).

That is, the drawbacks which have been encountered in the diffusion transfer process can be overcome or minimized by this invention, according to which development is carried out in the presence of both compounds (A) and (B).

Regarding the compounds (A), R is preferably methyl, ethyl, propyl or butyl and R is preferably hydrogen, methyl, ethyl, methoxy or ethoxy. They may 'be equally used with similar results. Therefore, those particular compounds which may be produced at a low cost and in a high yield normally be chosen.

As mentioned in the examples hereinafter, these compounds (A) and (B) may be directly added to a developing processing solution, but generally, they are added to a transfer layer or a layer thereon in a receiving sheet or a photosensitive emulsion layer or a layer thereon in a photosensitive sheet to ensure that the said compounds (A) and (B) substantially diffuse into the processing solution during developing and transfer. Therefore, it is difficult to specify the concentration of the compounds in the processing solution unless the amount of developer contained between the transfer sheet and photosensitive sheet during processing (this amount varies depending upon the strength of squeezing roller), amount of the compounds escaping from the sheet into developer contained in a large amount in a developing container (this amount varies depending upon the time in which the sheet is passed under the level of developer solution and diffusion speed), and the amount of the compounds (A) and (B) which once escape into the developer and are contained between the two sheets, etc. are constant. Furthermore, since processing in the diffusion transfer process is rapidly carried out and hence, the processing is completed before the compounds which ditfuse into the processing solution reach equilibrium, a suitable amount of the compounds to be added to the processing solution considerably varies depending upon temperature, composition of emulsion, presence of other additives, amount of silver halide solvent, amount of potassium bromide and cannot be definitely specified. Furthermore usually, additives which generally inhibit development are added to a photosensitive emulsion layer to improve preservability. Therefore, the content of such additives which inhibits development affects the necessary amount of the additives (A) and (B) used in this invention. However, the recommended amount of the additives (A) and (B) shown is as follows: In the case of adding them to a processing solution, the total amount of both compounds (A) and (B) will be about 0.01-l.0 g./l. and in the case of adding them a photosensitive sheet or receiving sheet the compounds (A) and (B) may be added to one of the sheets or to both sheets or, more detailedly, to an emulsion layer, a layer thereon a receiving layer or a layer thereon), the total amount of the compounds (A) and (B) will be about 0.00l0.18 g./m. It is preferable to add the additives (A) and (B) to the sheets because a small amount is suflicient in this case and moreover they can replenish the processing solution against the exhaustion of the toners.

EXAMPLE 1 Water I 4 Gelatin g Polyvinyl alcohol g 60 5% solution of copolymer of polyvinylmethyl ether and maleic anhydride (pH was 6'.) ..l.. 1 Finely divided cadmium sulfide dispersion (1%) After having copied a required drawing, the photosensitive sheet was fed into the developing solution with a receiving sheet face to face using a commercially available develop-transfer processor, which had been previously filled with a developer having the following formulation:

Hydroquinone g 12 1-phenyl-3-pyrazolidone g 1 Anhydrous sodium sulfite g 60 Sodium hydroxide g 12 Potassium bromide g 1.5 Sodium thiosulfate (crystal) ..g.. 10 3-ethyl-benzothiazoline-Z-thione g 0.2 5-phenyl-2-me2rcapto-1,3,4 oxadiazole g 0.1 Total amount with addition of water l 1 The surfaces of both sheets were put into contact 1-2 seconds after immerging of both sheets into the processing solution and squeezed. Excess processing solution was squeezed out by a pair of squeeze rollers and the sheets were taken out from the processor in a half-dried state. After a lapse of 1-5 seconds, they were separated to obtain dark negative images on the photosensitive layer and pure black and white clear positive images on the receiving layer.

When the above mentioned processing solution from which the additives used in this invention were omitted was used, the negative images were relatively rapidly formed in a black color, but images on the receiving sheet were not formed unless they were allowed to stand for about more than 45-60 seconds after being withdrawn from the processor, and furthermore, thus obtained positive images were yellow brown and had no commercial value.

When the above mentioned processing solution which contained only a compound (A) (3-ethyl-benzothiazoline- 2-thione) was used, transfer was rapidly effected and the color tone of the obtained images was pure black, but with under pressure, the white ground was stained, while with over exposure, fine lines were scratchy or lost.

When the 3-methyl derivative of the compound was used as the compound (A) the use thereof alone resulted in rapid transfer, but color tone of the images obtained was a warm tone of deep brown. When a compound B) was used together with the 3-methyl derivative of Compound (A), the color tone of the image obtained became nearly pure black.

EXAMPLE 2 Example 1 was repeated, except that the two additives in the processing solution were replaced by the following 4 additives.

3-methyl-benzothiazoline-Z-thione 0.15 3-propyl-benzothiazoline-Z-thione 0.15 5-(p-methyl-phenyl)-2-mercapto-1,3,4-oxadiazole 0.10 l-phenyl-S-mercapto-l,2,3,4-tetrazole 0.05

Similar results to those of Example 1 were obtained.

EXAMPLE 3 To the photosensitive emulsion layer of Example 1, were added l-phenyl-S-mercapto-1,2,3,4-tetrazole and 2- mercapto-benzothiazole in an amount of 0.01 g. and 0.01 g. per 11. of the emulsion, respectively.

A receiving sheet was prepared by applying to a thin white paper the same under-coating solution as in Example 1 and after drying it, applying thereon 30 g./m. of the In this case, it is not necessary to add the additives of this invention to the processing solution. Furthermore, it is desirable to decrease the amount of sodium thiosulfate. Therefore, the conventional commercially available processing solution for silver complex diffusion transfer process may be used as it is. In this example, the following solution was used.

Water I 1 Hydroquinone g 1-phenyl-3-pyrazolidone g 1 Anhydrous sodium sulfite g 70 Sodium hydroxide g Sodium thiosulfate (crystal) g 4 Potassium bromide g 2 EXAMPLE 4 A film base of polyethylene terephthate having a thickness of 0.05 mm. (Diafoll by Mitsubishi Plastics Industries Ltd.) was pre-coated as mentioned in Japanese Patent specification 410140 and then the following under-coating solution in an amount of about 50 g./m. was applied thereto as the binder having the composition of Japanese Patent specification 428151.

Formulation of under-coating solution.

Then, the following intermediate layer was applied in an amount of about 30 g./m.

Polyvinyl pyrrolidone g 30 Water l 1 10% polyacrylamide solution ml 100 Decolorizing dye (brown) g 2 Saponin solution (5%) 1-- 200 Furthermore, about 60 g./m. of high sensitive silver chloro-bromide gelatin emulsion for enlarging, wherein the greater part of gelatin was substituted by carboxymethyl starch was applied to the intermediate layer. (0.02 g./l. of benzotriazole was added to the photosensitive emulsion as an additive.)

Finally, 2% solution of carboxymethyl starch was thinly applied.

The thus obtained photosensitive material can be conveniently used for reproduction of a plan from a positive image reduced in microfilm or for obtaining a somewhat small intermediate drawing from a large drawing. Copying with camera or enlargement from a positive micro-film image was carried out directly on the photosensitive film obtained as mentioned above and then processing was effected for 30 seconds to 1 minute with the following processing solution, a negative image was formed on photosensitive layer and the undeveloped silver halide was diifused and transferred to the under layers with action of solvent to produce a positive image. Then, immediately, the layer was rinsed with water, whereby the upper layers were difiused and spread out and thus a positive image was extremely rapidly obtained.

In this method, no fixing was required and a short period of water rinsing was sufiicient. A pure black transparent drawing was obtained by immediately treating with an acidic methanol solution.

FORMULATION OF DEVELOPER G. 1-phenyl-3-pyrazolidone 1.0 Anhydrous sodium sulfite 75.0 Hydroquinone 10.0 Sodium hydroxide 15.0 Sodium thiosulfate (crystal) 50.0 Potassium bromide 2.0 3-propyl-'benzothiazoline-2-thione 0.10 5-methyl-2-mercapto-1,3,4-oxadiazole 0.05 Total amount was 1 l. by adding water. 2

EXAMPLE 5 ml. of 1% solution of 3-ethyl-benzothiazoline-2-thione in ethanol and 40 ml. of 1% solution of 5-phenyl-2- mercapto-1,3,4-oxadiazole were added to the under coating solution in Example 4, whereby the additives in the processing solution could be omitted with the same results as of Example 4. Furthermore, similar results were obtained by adding only 3-ethyl-benzothiazoline-Z-thione to the under coating solution and S-phenyl-Z-mercapto-1,3,4- oxadiazole to the photosensitive emulsion. In this case, benzotriazole in the photosensitive emulsion may be omitted or in place of benzotriazole, half the amount of l-phenyl-S-mercapto-1,2,3,4-tetrazole may be added.

EXAMPLE 6 A photosensitive sheet was produced by applying low sensitive silver chloride emulsion to a thin photographic base paper as in Example 1. On the photosensitive emulsion layer, an over layer having the following formulation and containing developing nucleus was applied in an amount of about 30 g./m. as in the receiving layer and then the obtained layer was dried.

FORMULATION OF THE OVER LAYER Water l 1 Carboxymethylcellulose (Na salt) g 15 Finely divided zinc sulfide dispersion (1%) ml 15 1% solution of 3methyl-benzothiazoline-Z-thione in ethanol ml 20 1% solution of 5-propyl-2-mercapto-1,3,4'oxadiazole in ethanol ml An original was copied with the said photosensitive sheet. An ordinary developing processor (a commercially available processor, for example, the processor for Hishirapid Processor) was modified so that only the photosensitive sheet was passed through a processing solution and the receiving paper was passed in a dried state in squeeze roller. As the receiving paper, a conventional writing paper or printing paper which had a water-proof property, but which underwent no special processing, was used. After a lapse of several seconds, the photosensitive sheet and the receiving paper were separated. The over layer of the photosensitive sheet which acts as a receiving layer and in this layer, a pure black positive image was formed was transfered on the surface of the receiving paper. Thus, a satisfactory correct positive copy was obtained on a conventional writing paper.

What is claimed is:

1. A development processing solution for a silver complex diffusion transfer process, which contains at least one of 3-alkyl-benzothiazoline-Z-thione derivatives having the following general formula (A) and at least one of 2- mercapto-l,3,4-oxadiazole derivatives having the following general Formula B l mT W-sn o T l wherein R is an alkyl group having not more than 5 carbon atoms, R is hydrogen, an alkyl group having not more than 3 carbon atoms or an alkoxy group having not more than 3 carbon atoms and R is an alkyl group having not more than 8 carbon atoms.

3. A receiving sheet for a silver complex diffusion transfer process, which contains at least one of 3-alkyl-benzothiazoline-2-thione derivatives having the following general Formula A and at least one of 2-mercapto-1,3,4- oxadiazole derivatives having the following general Formula B (B) wherein R is an alkyl group having not more than 5 carbon atoms, R is hydrogen, an alkyl group having not more than 3 carbon atoms or an alkoxy group having not more than 3 carbon atoms and R is an alkyl group having not more than 8 carbon atoms.

4. In a silver complex diffusion transfer process, the improvement which comprises carrying out the development in the presence of at least one of 3-alkyl-benzothiazoline-Z-thione derivatives having the following general Formula A and at least one of 2-mercapto-1,2,3- oxadiazole derivatives having the following general FormulaB O R; SH l l Rx N N wherein R is an alkyl group having not more than 5 carbon atoms, R is hydrogen, an alkyl group having not more than 3 carbon atoms or an alkoxy group having not more than 3 carbon atoms and R is an alkyl group having not more than 8 carbon atoms.

5. A photosensitive sheet according to claim 2, wherein the compounds (A) and (B) are contained in photosensitive emulsion layer or over layer.

6. A receiving sheet according to claim 3, wherein the compounds (A) and (B) are contained in receiving layer or over layer.

7. A processing solution according to claim 1 wherein the compounds (A) and (B) are contained in a total amount of 0.01-1.0 g./l.

8. A photosensitive sheet according to claim 2, wherein the compounds (A) and (B) are contained in a total amount of 0.001-0.18 g./m.

9. A transfer sheet according to claim 3, wherein the compound (A) and (B) are contained in a total amount of 0.001-0.18 g./m.

10. A method according to claim 4, wherein the compounds (A) and (B) are contained in the processing solution in the receiving sheet, in the photosensitive sheet or in both sheets.

References Cited UNITED STATES PATENTS 3,020,155 2/ 1962 Yackel et al. 9629' 3,257,206 6/1966 de Haes 9629 3,017,270 1/ 1962 Tregillus et al. 96-29 FOREIGN PATENTS 1,101,927 2/1968 England 9629 I. TRAVIS BROWN, Primary Examiner I. L. GOOD-ROW, Assistant Examiner U.S. Cl. X.R. 9652, 76 

